IIRC some programs (and med schools BTW), regardless how long you've been out of school or what your major was, will rigidly require at least one from an undergrad premed science professor. You really haven't mentioned how long it's been since you graduated, but a general rule of thumb is if you've been out for 4 years or more you can get appropriate letters from other than undergrad professors. I'd been out of school for 7 years, and used letters from my immediate supervisor, my former boss (hospital administrator) and a head QA nurse with whom I'd worked . Make sure your LOR writers are people who can adequately comment on your potential as a physician and your desire/commitment to medicine.
My recommendation: call the programs you're interested in, explain your background, and ask who they'd like to hear from. Consider carefully those programs with LOR policies inflexible enough to accommodate someone who?s been out of school for a while; they may not be appropriate programs for you to matriculate at.
Good luck!